The many variables make it difficult to accurately estimate the age
of cave deposits. We have no way of determining past conditions which
have influenced the rate of development. Oh, we know the formations are
many thousands of years old, beyond that we can only guess. Some
crude examples of known age are the tiny, one-half-inch
stalactites formed in the exit tunnel since it was completed some 30
years ago (see illustration on this page). Bathed in warm, dry air from
the outside, they have probably developed much faster than those inside
the main cave. Other active formations deep in the cave show very little
visible depositing over names written on them by early explorers in the
1880's. So the true secret of the age of the formations must rest with
the cave itself. Perhaps this is best.

Other Cave Features

An obvious feature you may see in Neptune's Grotto is
the brown lace work on the walls. They are lines of clay. Molecular
attraction causes the clay particles to cling together into what we call
clay worms. (See illustrations on page 27). Where does the clay
come from? Some of it may be washed in from the ground above. The rest of it is
the remnant of marble solution. Oregon Caves marble is 93 percent
calcium carbonate. The remaining 7 percent is non-soluble clay and
remains in the cave after the calcium carbonate is carried away in fluid
state. Clay worms are temporary features; vadose water or the touch of a
careless hand can easily remove them.

Speleogen above River Styx

Stalactites formed since exit tunnel was
completed in 1933

In the Ghost Room we find an interesting object.
Projecting from the ceiling is an 8-inch thick slab of angular brown
rock. Its edges have been broken, rather than dissolved. This is a
clastic dike. Evidence is lacking to definitely state its origin
or manner of emplacement. But at some time in the past, there was an
extensive crack in the marble which was filled by a mudlike material
made up of bits of quartz, plagioclase, horneblende, epidote, clay, and
other minor ingredients. It may have been washed in from the surface, or
it could have been injected from below by earthquake shocks which
cracked the marble and forced the pliable material into the cracks.

Eventually it hardened into rock. Due to its
non-soluble ingredients, the dike was not dissolved when the Ghost Room
was formed. Like the "blades" we discussed previously, it remained as a
projection into the room while the marble walls receded under solution
activity. Being brittle, it has apparently been broken off periodically
by the jar of earthquakes or cave collapse.

Another obvious discrepancy in the marble framework
of the caves is the thin layer of slate found in the 65-foot tunnel.
This reveals an interruption in the limestone sedimentation of the
Triassic sea. A thin layer of shale was deposited between limestone
layers. Later, when the limestone became marble, the shale became
slate. It should be mentioned here that limestone and shale vary greatly
in their contents and often inter-blend with each other. "Pure"
limestone is white. Different shades occur with different amounts of
claylike impurities. When the impurities over shadow the limestone, then
the rock may be called shale. The whitest marble in Oregon Caves came
from the purest limestone. The darker, blue-banded marble is rich in
slate impurities.